The purpose of this study is to evaluate an overnight system that will turn off the insulin pump automatically if the system predicts that a low blood sugar is likely. The study system includes a combination continuous glucose monitor (CGM)/ insulin pump made by Medtronic MiniMed, Inc and a regular laptop computer that runs a computer program that predicts low blood sugar. It works by (1) measuring the glucose levels under the skin with a continuous glucose monitor, (2) using a computer program on a laptop to predict what will happen to the glucose level over the next 35-55 minutes, and (3) turning off the insulin pump when the computer program predicts that low blood sugar will occur. We have tested this system overnight in the hospital and are ready to test the system in the home environment to learn more about how well it will work and to make sure that the blood sugar does not go too high when the pump shuts off.